Capacitor Pulse Forming Network with Multiple Pulse Inductors

ABSTRACT

Capacitor based pulse forming networks and methods are provided which require fewer inductors are that pulsed more frequently to provide a smaller, lower mass, and lower inductance pulse forming network having better pulse shaping characteristics than conventional pulse forming networks. In one implementation, the invention can be characterized as a capacitor based pulse forming network comprising a plurality of inductors adapted to be coupled to a load, a plurality of capacitor units, and a plurality of switches. Each switch couples a respective capacitor unit to a respective inductor, wherein multiple capacitor units are coupled to each inductor by separate switches. The plurality of switches are adapted to non-simultaneously discharge at least some of the multiple capacitor units to provide non-simultaneous pulses through a given inductor to the load and not through other inductors. The non-simultaneous pulses form at least a portion of an output pulse waveform to the load.

This application is a continuation-in-part of U.S. application Ser. No.11/274,060, filed Nov. 14, 2005, for CAPACITOR PULSE FORMING NETWORKWITH MULTIPLE PULSE INDUCTORS, which is a continuation of U.S.application Ser. No. 10/772,748, filed Feb. 4, 2004, for CAPACITOR PULSEFORMING NETWORK WITH MULTIPLE PULSE INDUCTORS, now U.S. Pat. No.6,965,215, both of which are incorporated in their entirety herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to capacitor-based high energypulse forming networks.

2. Discussion of the Related Art

In certain applications where high power sources (e.g., power lines,batteries) are unable to deliver high levels of peak power, pulseforming networks having high-energy density capacitors are often used.In these applications, the capacitors are slowly charged from the powersource and then quickly discharged for short time periods to providepulsed energy at high peak power levels. The capacitors are typicallyused with large inductors to restrict the flow of energy from thecapacitors and to establish the frequency, period and shape of theoutput pulse from the network.

FIG. 1 illustrates a known pulse forming network 100 including a numbern of modules 102 _(n) (where n=1, 2, . . . , N) coupled to a load 104.Each module 102 _(n) includes a bank of capacitors 106 _(n) coupled tothe load 104 through an inductor 110 _(n) via a switch 108 _(n) and ananti-reversing diode 112 _(n). In operation, each bank of capacitors 106_(n) is charged while the switches 108 _(n) are open. Once charged,groups of modules 102 _(n) are sequentially discharged to the load 104.For example, initially, a predetermined number of modules (a first setof modules) are discharged at once to the load 104. That is, theswitches 108 for the first set of modules are closed at once,discharging the energy stored through the inductors 110 corresponding tothe first set of modules to the load producing a current pulse to theload 104. At a point in time after the discharge of the first set ofmodules is initiated, a second set of modules 102 are discharged at onceto the load producing a second current pulse to the load. After theinitiation of the discharge of the second set of modules, a third set ofmodules is discharged at once to the load producing a third currentpulse, and so on. The pulses add, creating the output pulse waveform atthe load. The anti-reversing diodes 112 _(n) of each module 102 _(n)prevent the voltage from reversing on the capacitors (which prevents thecapacitors from recharging from their own discharge current) and ensurethat the current discharging from other sets of modules flows to theload 104. Typically, in most high power pulse forming networks, thereare 3-5 sets of modules, each set being discharged at the same time, thesets being discharged in sequence.

FIG. 2 is a graph of current over time illustrating a typical pulsewaveform formed by the pulse forming network 100 of FIG. 1 including 72modules (i.e., N=72) divided into 3 sets of modules. For example,modules 102 ₁-102 ₂₄ are then discharged at the same time formingcurrent pulse 202, modules 102 ₂₅-102 ₄₈ are then discharged at the sametime forming pulse 204, and modules 102 ₄₉-102 ₇₂ are discharged at thesame time forming pulse 206. The pulses add to produce waveform 208 ascompared to the desired flat top waveform 201, emulating a square orrectangular pulse.

This pulse forming network results in many inductors (e.g., 72 in thisexample) representing a large mass in the pulse forming network.Furthermore, the waveform 208 does not accurately track the desired flattop waveform 201, especially at the end of the waveform. Additionally,significant energy is wasted at the end of the waveform (which isillustrated as area 212 under the curve of waveform 208). Accordingly,the energy storage requirements of the pulse forming network 100 must beincreased in order to provide enough current in view of the wastedenergy. Requiring many large inductors and needing to provide additionalenergy storage due to wasted energy adds to the mass and size of thepulse forming network, as well as increases the flux generated by theinductors.

SUMMARY OF THE INVENTION

The invention provides a capacitor based pulse forming network in whichfewer inductors are pulsed more frequently to provide a smaller, lowermass, and lower inductance pulse forming network having better pulseshaping characteristics than conventional pulse forming networks.

In one embodiment, the invention can be characterized as a capacitorbased pulse forming network comprising: a plurality of inductors adaptedto be coupled to a load; a plurality of capacitor units; and a pluralityof switches, each switch coupling a respective capacitor unit to arespective inductor, wherein multiple capacitor units are coupled toeach inductor by separate switches. The plurality of switches areadapted to non-simultaneously discharge at least some of the multiplecapacitor units to provide non-simultaneous pulses through a giveninductor to the load and not through other inductors. Thenon-simultaneous pulses form at least a portion of an output pulsewaveform to the load.

In another embodiment, the invention can be characterized as a methodfor providing a pulse waveform to a load, and a means for accomplishingthe method, the method comprising the steps of: charging a plurality ofcapacitor units, wherein multiple capacitor units are coupled to each ofa plurality of inductors, each inductor coupled to the load; andnon-simultaneously discharging at least some of the multiple capacitorunits to provide non-simultaneous pulses through a given inductor to theload and not through other inductors; wherein the non-simultaneouspulses form at least a portion of the pulse waveform.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following more particulardescription thereof, presented in conjunction with the followingdrawings.

FIG. 1 is a diagram of a conventional pulse forming network whichdischarges energy storage capacitors through inductors.

FIG. 2 is a graph illustrating a typical pulse waveform formed by thepulse forming network of FIG. 1.

FIG. 3 is a diagram of a pulse forming network according to oneembodiment of the invention.

FIG. 4 is a graph illustrating an output pulse waveform produced by oneembodiment of the pulse forming network of FIG. 3.

FIG. 5 is a diagram of an energy storage module of the pulse formingnetwork of FIG. 3 including a charging power supply and a timingcontroller in accordance with one embodiment of the invention.

FIG. 6 is a diagram of a portion of the timing controller of FIG. 5 forcontrolling the discharging of a capacitor unit of the pulse formingnetwork of FIG.3 according to one embodiment of the invention.

FIG. 7 a flowchart illustrating the steps performed in accordance withone embodiment of the invention.

FIG. 8 is a diagram of a pulse forming network according to anotherembodiment.

FIG. 9 is a schematic diagram of a rail gun application using a pulseforming network to provide energy to launch a projectile in accordancewith several embodiments.

FIG. 10 is a diagram of a pulse forming network with an active shuntcircuit according to a further embodiment for use in an application inwhich excess energy at the end of the pulse waveform is to be removed.

FIG. 11 is a diagram of a pulse forming network with an active shuntcircuit according to another further embodiment for use in anapplication in which excess energy at the end of the pulse waveform isto be removed.

FIG. 12 is a diagram of a pulse forming network in accordance withseveral embodiments in which one or more stages or modules of thenetwork resembles a traditional pulse forming network stage.

FIG. 13 is a diagram of one embodiment of the pulse forming network ofFIG. 12 for use in a rail gun application.

FIG. 14 is a graph of the capacitor voltage of the capacitor units ofthe pulse forming network of FIG. 13 over time in accordance with oneembodiment.

FIG. 15 is a graph illustrating the current pulses provided by the pulseforming network of FIG. 13 over time including the output pulse waveformin accordance with one embodiment.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION

The following description is not to be taken in a limiting sense, but ismade merely for the purpose of describing the general principles of thepreferred embodiments. The scope of the invention should be determinedwith reference to the claims.

Referring first to FIG. 3, a diagram is shown of a pulse forming networkaccording to one embodiment of the invention. Referring also to FIG. 4,a graph is shown illustrating an output pulse waveform produced by oneembodiment of the pulse forming network of FIG. 3.

The pulse forming network 300 includes multiple capacitor units beingswitched through each inductor. Specifically, the pulse forming network300 includes a plurality (e.g., three) energy storage modules 302, 304,306 each coupled to a load 104. Each module 302, 304 and 306 includes aplurality (e.g., four) of capacitor units coupled to the load 104through an inductor via a switch. Each module 302, 304, 306 alsoincludes an anti-reversing diode (although in some embodiments, ananti-reversing diode is not present in all modules, for example, seeFIG. 10). As illustrated, module 302 includes capacitor units 308, 309,310 and 311, each coupled via one of switches 312, 313, 314 and 315through inductor 316 to the load 104. Similarly, module 304 includescapacitor units 318, 319, 320 and 321, each coupled via one of switches322, 323, 324 and 325 through inductor 326 to the load 104. And module306 includes capacitor units 328, 329, 330 and 331, each coupled via oneof switches 332, 333, 334 and 335 through inductor 336 to the load 104.Anti-reversing diodes 340, 342 and 344 are coupled to each module 302,304 and 306 to prevent the voltage from reversing on the capacitors andassure unidirectional current flow through the switches. This alsominimizes the circulating current from one module to enter anothermodule.

According to several embodiments of the invention, the capacitor unitsof a given module are individually switched (discharged) through thesame inductor at different times such that the same inductor is pulsedmultiple times when forming the output pulse waveform (i.e., multipledischarge pulses are provided to the load 104 through the same inductorto the load 104 and not through the other inductors of the othermodules). Thus, in a broad sense, multiple capacitor units arenon-simultaneously discharged through each inductor of the network 300.Thus, each inductor is pulsed at a higher frequency than in traditionalpulse forming networks. As described more fully below, this results inthe use of fewer and smaller inductors, fewer anti-reversing diodes,better pulse shaping capabilities and overall reduction in size and massrelative to known pulse forming networks. It is noted that whenreferring to a discharge pulse flowing through a given inductor and notthrough the inductors of other modules, the discharge current throughthe given inductor flows generally directly to the load and does notflow through the other inductors on its path to the load. For example,in the illustrated embodiment, multiple inductors are not coupled inseries to the load. However, it is understood that the discharging ofany given capacitor unit will result in a small amount of stray inducedcurrents in the other inductors, which is unavoidable. Accordingly, inpreferred embodiments, the discharge current (not including strayinduced current) flows through the given inductor and not through theother inductors. It is also noted that in many embodiments, theinductors may be made smaller since they are pulsed more frequently, andin some cases, a discrete inductor is not needed. For example, in someembodiments, the wireline or cabling connection from a given switch tothe load provides a natural inductance, which in some cases is adequate.Thus, even though an inductor is illustrated in the various figurespresented herein, it is understood that in some cases the illustratedinductor represents an inductance and not necessarily a discreteinductor. As such, as used herein, the term inductor is understood to bea discrete inductor or an inductance.

According to further embodiments, at least some of, but not all of thecapacitor units of a given module are individually switched (discharged)through the same inductor at different times such that the same inductoris pulsed multiple times when forming the output pulse waveform. Thus,in a broad sense, at least some of multiple capacitor units coupled toeach inductor of the network 300 are non-simultaneously dischargedthrough that inductor. In cases where not all of the pulses arenon-simultaneously discharged, at least two of the multiple capacitorunits coupled to a given inductor are simultaneously discharged. Forexample, capacitor units 308 and 309 could be simultaneously dischargedwhile all remaining capacitor units are non-simultaneously dischargedwith respect to each other and capacitor units 308 and 309. Eachinductor is still pulsed at a higher frequency than in traditional pulseforming networks, which also results in the use of fewer and smallerinductors, fewer anti-reversing diodes, better pulse shapingcapabilities and overall reduction in size and mass relative to knownpulse forming networks. The combination of non-simultaneous andsimultaneous pulses through a given inductor depends on the applicationand pulse shape that is desired.

In operation, each of the capacitor units are charged to the appropriatevoltage by a high voltage charging supply (such as illustrated in FIG.5). In order to generate a waveform having a desired shape, thecapacitor units are sequentially discharged in a predetermined sequenceto produce that an output pulse waveform having the desired shape, suchthat the capacitor units of a given module are individually dischargedat different times through the inductor of the given module, i.e.,non-simultaneously discharged in several embodiments.

For example, in preferred embodiments, at the start of the pulse, switch312 of module 302 is closed to discharge capacitor unit 308 through theinductor 316 to the load 104 and not through inductors 326, 336. Thisresults in pulse 403 of FIG. 4. At a predetermined time after theclosing of switch 312 (i.e., after beginning the discharge of capacitorunit 308), switch 322 of module 304 is closed to discharge capacitorunit 318 through the inductor 326 to the load 104 and not throughinductors 316, 336, which results in pulse 404 of FIG. 4. Proceeding insequence, switch 332 of module 306 is closed to discharge capacitor unit328 through the inductor 336 to the load 104 and not through inductors316, 326, which results in pulse 405 of FIG. 4. It is noted that switch312 is now open. The switching sequence then continues back to module302, such that switch 313 is closed to discharge capacitor unit 309through the inductor 316 to the load 104 and not through inductors 326,336, which results in pulse 406 of FIG. 4. It is preferred that the eachcapacitor unit of a given module completely discharge prior to the nextcapacitor unit of that module discharging, i.e., the pulses through agiven inductor do not overlap in time. Thus, the switching timing ispreferably such that pulse 406 starts after the end of pulse 403, and soon. However, in alternative embodiments, depending on the application,pulses through a given inductor may be made to overlap in time. In suchalternative embodiments, one or more switches in a given module areclosed such that at least a portion of the pulses going through theinductor of that module overlap each other. For example, a givencapacitor unit of a given module is discharged before a voltage of analready discharging capacitor unit of that module reaches zero. This canbe helpful in shaping the pulse to a desired shape for a givenapplication. For example, if additional energy is required at a portionof the pulse, then more switches (even in the same module) are closed.

Accordingly, in one embodiment, the switching sequence is such that theswitches close in the order of 312, 322, 332, 313, 323, 333, 314, 324,334, 315, 325 and 335 in order to sequentially discharge capacitor units308, 318, 328, 309, 319, 329, 310, 320, 330, 311, 321 and 331 in order.Thus, current pulses 403, 404, 405, 406, 407, 408, 409, 410, 411, 412,413 and 414 are sequentially produced in time at the load. The sum ofthe pulses 403-414 adds to the output pulse waveform 402, which moreclosely follows the desired flat top waveform 201 than the traditionalnetwork of FIGS. 1-2. Such waveforms are needed for various types ofloads, including charged particle accelerators, microwave sources andlasers. Thus, in preferred embodiments, a first capacitor unit of eachmodule is sequentially discharged, then a second capacitor unit of eachmodule is sequentially discharged, then a third capacitor unit of eachmodule is sequentially discharged, and so on until all capacitor unitsof all modules are discharged. Such sequence ensures that the capacitorunits of each module are non-simultaneously discharged.

In one variation of a switching sequence, the first several capacitorunits of the sequence are switched or pulsed at the same time in orderto decrease the rise time of the pulse. This is advantageous in creatinga flat top waveform. For example, switches 312 and 322 are closed at orvery near the same time to discharge capacitor units 308 and 318 throughinductors 316 and 326, respectively. After this initial pulsing, thesequence proceeds as described above, with the desired interval inbetween discharge pulses. In other embodiments, some capacitor units,other than the first and several capacitor units, in the same circuitwith a given inductor or coupled to different inductors, are switched orpulsed at the same time (simultaneously). For example, depending on theapplication, other capacitor units in the middle of the pulse waveformare pulsed at the same time (simultaneously). This provides additionalenergy at times needed for the application.

It is noted that in preferred embodiments, only one capacitor unit of agiven module is switched through the inductor of that module at a time.Accordingly, less energy is switched through the inductor relative totraditional pulse forming networks. Therefore, the inductor has smallerinductance requirements, i.e., a smaller value inductor having less sizeand mass may be used in each module. In preferred embodiments, only oneof the switches of a given module are closed at a time, while the otherswitches are open. For example, after switch 312 closes and completelydischarges the capacitor unit 308, switch 312 naturally re-opens as aresult of zero current flowing therethrough. In another example, switch312 re-opens due to a commutation circuit that is coupled to switch 312which forces the switch to re-open. In another example, if the switch312 is conducting when switch 313 is closed, the closing of switch 313will reverse the current through switch 312 to shut off or re-openswitch 312. If switch 312 can be commutated, the closing of switch 313acts as a commutation circuit to shut off switch 312.

Advantageously, since each inductor in the pulse forming network ispulsed multiple times (i.e., energy for multiple capacitor units isdischarged through the same inductor) when forming the output pulsewaveform, fewer inductors are required compared to a traditional pulseforming network that requires a single inductor for many modules, suchas shown in FIG. 1. In FIG. 3, each inductor is pulsed 4 times peroutput pulse waveform, e.g., inductor 316 is pulsed 4 times (bydischarges from each capacitor unit 309, 309, 310 and 311), producingpulses 403, 406, 409 and 412. In contrast, in FIG. 1, each inductor ispulsed once per output pulse waveform. Accordingly, the pulse formingnetwork 300 of FIG. 3 including only three inductors can replace thepulse forming network of FIG. 1 having 72 inductors at the same energylevel. This savings in the number of inductors represents a dramaticreduction in the size and mass of the pulse forming network. It is wellknown that inductors are the second largest mass component aside fromthe energy storage capacitor units in a pulse forming network.

It is noted that a pulse forming network in accordance with severalembodiments of the invention may be implemented with as few as twoinductors (i.e., two energy storage modules), each inductor (of eachmodule) pulsed multiple times by different capacitor units to form theoutput pulse waveform. However, in order to ensure that a givencapacitor unit (of a given module) is fully discharged prior todischarging the next capacitor unit coupled to the same inductor (of thesame module), it is desired that the pulse forming network preferablyhave three or more inductors (thus, three or more modules as defined).It is noted that in some embodiments, pulses through a given inductorare intended to overlap, i.e., a given switch coupling a given capacitorunit to a given inductor is closed prior to the complete discharging ofa currently discharging capacitor, or prior to the completion of currentthrough the given inductor from a previously discharged capacitor unit.However, depending on the capability of the switches, a blocking diodemay be needed to prevent the switch from burning out (see FIG. 8).Additionally, it is noted that a pulse forming network in accordancewith several embodiments of the invention may be implemented with as fewas two capacitor units coupled to each inductor; however, in preferredembodiments, four or more capacitor units are coupled to each inductor.

Furthermore, since each inductor in the pulse forming network is pulsedat a higher frequency and switching smaller amounts of capacitance at agiven time, the inductors themselves may be made smaller to handle lessenergy at a given time. This further reduces the size and mass of theinductors in the network relative to a traditional network, such asillustrated in FIG. 1.

The capacitor units of FIG. 3 may each comprise one or more capacitors.That is, each capacitor unit may be a single capacitor or may be a bankof capacitors in series and/or in parallel configured to provide theproper amount of energy storage. The energy storage capacitors typicallycomprise the largest size and mass components of the pulse formingnetwork. Additionally, these capacitor units may be charged to differentvoltage levels. Such levels will be dictated by the shape of the pulsewaveform to be produced by the network. For example, a particular shapewaveform may be needed or the impedance of the load 104 may vary, suchthat changing the voltage level that some of the capacitor units arecharged to will produce desired results. For example, in applicationsthat require a fast shut off time (such as in a rail gun application),the charge voltage of the last few capacitor units (e.g., capacitorunits 311, 321 and 331 in the sequence of FIG. 4) may be different thanthe preceding capacitor units. In some embodiments, where a fast shutoff time is desired with little residual energy at the end of the pulsewaveform, the last several capacitors are charged to a higher voltagethan preceding capacitor units, such that the capacitance is lowered andthe current through the inductor ends sooner. Thus, in a general sense,in some embodiments, one or more of the capacitor units of the pulseforming networks described herein are intentionally charged at differentvoltage levels. In some applications, depending on the shape of thepulse waveform to be produced, it is desired that some of the capacitorunits are charged to a higher voltage level where rise and fall ofcurrent is quickly needed, whereas some of the capacitor units arecharged to a lower voltage level where rise and fall of current isdesired to occur more slowly. In some embodiments, there may be severaldifferent levels of voltage charge for different capacitor units. Thesevoltage levels may be needed to help shape a particular pulse waveformor to help match the output pulse waveform to a varying impedance load.In rail gun applications and other applications where a faster shut offtime is needed relative to the rise time of the pulse waveform, thevoltage level of capacitor units discharging early in the sequence arecharged to a lower voltage level that those capacitor units discharginglater in time in the pulse waveform. In embodiments using semiconductorstacks to function as the switches, this allows for fewer switchingdevices (e.g., thyristors) that make up a given switch.

The switches illustrated in the energy storage modules 302, 304, 306 ofFIG. 3 may each comprise one or more switches. Depending on theembodiment, the switches may be any type of switching device, preferablya switching device that can shut off (or be shut off). For example, theswitches may be solid state switches, such as silicon controlledrectifiers (SCR), gate-turn-off switches (GTO), bipolar junctiontransistors (BJT), field effect transistors (FET), insulated-gatedbipolar transistors (IGBT) or other transistor. For example, in oneembodiment, each switch comprises a transistor and a diode in series(see FIG. 8) such that it behaves as an SCR. The switches may also beelectromechanical switches, such as a spark gap, if the pulsingfrequency is sufficient to allow the switch to turn off between pulsesof the same inductor (of the same module). Even if the switch has notturned off yet, in preferred embodiments, the closing of the next switchin the same module will act to shut off the previous switch.

In comparison to traditional pulse forming networks, in manyembodiments, the number of switches increases. However, the total energyswitched will remain the same and the size and mass of the switches isnormally significantly less that the size and mass of the inductors.Thus, even though there may be more switches present, the overall massand size of the pulse forming network is reduced due to the reduction inthe number and size of inductors and a reduction in the number ofanti-reversing diodes.

It is also noted that compared to known pulse forming networks, theswitches are grouped together. For example, in FIG. 1, each illustratedswitch is a grouping of switches. Whereas according to severalembodiments, the switches are spatially distributed within a givenmodule to individually switch capacitor units. Since the switches aredistributed throughout a given module, the switches are easier to coolthan if the switches are bunched together. In preferred embodiments, theswitches are mounted on the capacitor units, the capacitor units used tocool the switches.

Additionally, as illustrated in FIG. 3, one anti-reversing diode 340,342, 344 is coupled to each inductor 316, 326, 336 in each energystorage module 302, 304, 306. These anti-reversing diodes (also referredto as free-wheeling diodes) primarily function to limit voltage reversalon the capacitors, which may cause the current discharged from a givencapacitor unit into the inductor of that module from flowing backthrough the switch into the capacitor. Thus, the anti-reversing diodeslimit current oscillation between the capacitor units and the load.These anti-reversing diodes also minimize current discharge from othermodules from discharging into each module such that substantially alldischarge current flows to the load 104, not including induced straycurrents in the other inductors. That is, the discharging of onecapacitor unit induces a small amount of stray current in the otherinductors; however, this induced stray current is different than thedischarge current from the capacitor unit. It is also noted thatgenerally, anti-reversing diodes are not required in order to minimizecurrent discharge from other modules from discharging into each module,since the impedance of the load 104 is generally very small relative tothe impedance of the other modules. That is, the discharge currentnaturally flows through a given inductor directly to the load, and notthrough the other inductors of the other modules. Relative to the knownpulse forming network of FIG. 1, since there are fewer inductorsrequired, there are likewise fewer anti-reversing diodes required. Inthe example provided, 3 diodes are used in the network 300 compared to72 diodes used in FIG. 1. This again results in a savings of size andmass in the pulse forming network 300.

In some embodiments, the anti-reversing diodes 340, 342 and 344 may bedamaged by driving current through them in the opposite direction. Thatis, when the voltage of discharging capacitor unit 308 reaches zero,current starts flowing through the anti-reversing diode 340. If anothercapacitor unit is discharged while this current is flowing, it can causecurrent to flow in the opposite direction in the anti-reversing diode340, which can damage the anti-reversing diode 340. In one embodiment,when an anti-reversing diode is conducting, no additional capacitorunits are switched on. For example, the next capacitor unit is switchedon after the anti-reversing diode 340 has shut off (i.e., space thepulses apart). In another example, the next capacitor is switched onbefore the anti-reversing diode begins to conduct. That is, in oneembodiment, as soon as the voltage of capacitor unit 308 reaches zerovolts (or just before it reaches zero volts), capacitor unit 309 isswitched on, and when capacitor unit 309 reaches or approaches zerovolts, capacitor unit 310 is switched on. Likewise, when capacitor unit310 reaches or approaches zero volts, capacitor unit 311 is switched on.When capacitor unit 311 reaches zero volts, the anti-reversing diode 340will conduct, but this is not problematic since there are no otherpulses that will go through the given inductor. If the circuit switchesa given capacitor unit on a little early (just before the previouslyswitched capacitor unit reaches zero volts), there is no current throughdiode 340 and a trap charge is left on the previous capacitor. If thecircuit switches a given capacitor unit on a little late (just after thepreviously switched capacitor unit reaches zero volts), a small amountof current flows through diode 340 but not enough to damage the diode340.

It is also shown that the pulse forming network 300 according to manyembodiments of the invention improves pulse shaping abilities relativeto known pulse forming networks. For example, the output pulse waveform402 of FIG. 4 more closely emulates the desired flat top output waveform201 than does waveform 208 of FIG. 2. Furthermore, depending on thetiming of the discharge switches, the designer may be able to accuratelycreate many different pulse shapes. For example, while a square orrectangular waveform is described herein as being preferred, it isunderstood that it may be desired to output a triangular waveform, awaveform that ramps up or down, or other desired pulse shape dependingon the application requiring the pulse. Thus, by varying the timing ofdischarge pulses relative to each other (controlling the switchingsequence and timing), the shape of the output waveform may be varied.

The higher pulsing frequency of each inductor also provides for fasterrise times according to several embodiments. That is, as seen bycomparing FIGS. 2 and 4, it takes less time to go from 10% to 90% of thepeak current in FIG. 4 than in FIG. 2. Faster rise times are importantin microwave applications where it is desired to quickly turn on aradiation source. The ability to emulate the ideal waveform more closelyresults in less energy wasted in the network 300. Wasted energy is notpreferred since the pulse forming network must be appropriately sizedand charged to provide the needed energy as well as the un-usable wastedenergy. Therefore, wasting less energy results in the ability to designa network that more closely matches the energy requirements of the load.

The higher pulsing frequency of each inductor also provides for fastershut off times according to several embodiments. Advantageously, thisresults less wasted energy at the end of the output pulse waveform. Thiswasted energy is illustrated as area 212 in FIG. 2. In contrast,depending on the timing of the discharge pulses, this wasted energy canbe significantly decreased, made negligible, or eliminated. Inapplications such as launching electromagnetic weapons, such as railguns excess wasted energy at the end of the pulse waveform can result inmuzzle flash. By reducing or eliminating this wasted energy, flashsuppressors are not required. Additionally, recovery systems (such asthose used in rotating machinery based devices) are not required. Again,wasted energy is energy that must be stored by the pulse forming network300, but which is not used. Thus, if there is less wasted energy, theenergy storage components of the network 300 may be sized most closelyto the requirements of the load, without having to be oversized toaccount for wasted energy.

Many of the advantages described above result in a pulse forming networkthat can be reduced in size, mass and cost while providing betterperformance and efficiency. For example, the inductor requirements arereduced (in terms of the number and size/mass of inductors), the dioderequirements are reduced (since there are fewer inductors, fewer diodesare required), and there is a reduction in the amount of wasted energy,particularly at the end of the output waveform (which results in areduced energy storage requirement and a smaller network).

Referring next to FIG. 5, a diagram is shown of an energy storage moduleof the pulse forming network of FIG. 3 including a charging power supplyand a timing controller in accordance with one embodiment of theinvention. Although the circuit of FIG. 3 is generalized, it isunderstood that additional components are needed to fully operate thepulse forming network 300. For example, a charging circuit 502 iscoupled to each capacitor unit of the network (e.g., to capacitor units308, 309, 310 and 311 as illustrated). Additionally, a timing controller504 is coupled to each discharge switch in this module as well as theother modules (e.g., switches 312, 313, 314, 315, 322, 323, 324, 325,332, 333, 334 and 335) in order to control the discharging sequence. Itis understood that although only one module (e.g., module 302) isillustrated, all modules are similarly coupled to the charging circuit502 and the timing controller 504.

The charging circuit 502 includes a charging power supply 506 that iscoupled to each capacitor unit through a respective charging resistor508 and a respective charging switch 510. For example, as illustrated, aseparate charging power supply 506 is coupled to each capacitor unit. Inoperation, the charging switches 510 are closed while the dischargingswitches (e.g., switches 312, 313, 314, 315) are open. This allowscharging current from the power supplies 506 to charge the capacitorunits to the proper voltage. Such charging circuits are well known inthe art.

The timing controller 504 provides the necessary signaling to cause thesequential switching of the discharge switches in each module in orderto discharge the capacitor units in sequence, such that the inductorsare pulsed at a higher frequency than is traditionally done. In oneembodiment, the timing controller 504 comprises a timing circuitincluding many 555 timers, a portion of which is illustrated in FIG. 6.A 555 timer is a well known integrated circuit used in applicationsrequiring precision timing, pulse generation, sequential timing, timedelay generation and pulse width modulation. A 555 timer includes twovoltage dividers, a bi-stable flip flop, a discharge transistor and aresistor divider network.

Referring to FIG. 6, a diagram is shown of a portion of the timingcontroller 504 of FIG. 5 for controlling the discharging of a capacitorunit of the pulse forming network of FIG.3 according to one embodimentof the invention.

In preferred embodiments, the timing circuit includes two 555 timers perdischarge switch in the pulse forming network. The portion 600 of thetiming circuit includes two 555 timers: timer 602 which controls thetiming sequence and timer 604 which holds the switch closed during theremaining discharge sequences. Timer 602 has a capacitor C1 and avariable resistor R1 (e.g., a potentiometer) coupled thereto (at theThreshold and Discharge pins), while timer 604 has a capacitor C2 and afixed resistor R2 coupled thereto. Power (V_(CC)) is supplied to allcomponents. Generally, every 3 RC time constants, a 555 Timer changesstate. An input trigger signal 606 is received at the timer 602 (at thetrigger pin), which is used to determine the timing between pulses,while timer 604 turns on (i.e., closes) a discharge switch. For example,the output 608 of timer 602 becomes the input trigger signal to thefirst one of the next pair of 555 timers in the timing circuit thatcorresponds to the next sequential capacitor unit to be discharged. Theoutput 608 of timer 602 is also input as the input trigger signal (atthe trigger pin) to timer 604. Capacitor C3 and resistor R3 allow theoutput signal 608 to trigger the timer 604 and to trigger the next pairof timers in the sequence. The output 610 of timer 604 is used toactivate the closing of a particular switch (and the discharging of aparticular capacitor unit) and hold it in that position for a specifiedinterval. The output 610 is amplified at amplifier 612 (e.g., an op-amp)to become the discharge timing signal 614 that is coupled to therespective switch of the network. Again, the output 608 becomes theinput trigger signal 606 of the next set of timers corresponding to thenext switch and capacitor unit to be discharged.

In this embodiment, each discharge switch (e.g., switch 312) comprises atransistor and a diode in series that behave as a silicon controlledrectifier (SCR) in that the switch shuts off (i.e., opens) when thedischarge current from the capacitor unit reaches zero. In thisembodiment, each switch of a given module is allowed to stay open inbetween switching so that a given capacitor is not re-charged by thedischarge of another capacitor of the same module.

In order to cause the proper timing in the discharge sequence, thevalues of capacitors C1 and C2, variable resistor R1 and fixed resistorR2 are selected. Gross timing changes may be made by changing thecapacitance C1 and C2, while fine timing changes may be made by changingthe variable resistor R1 and the fixed resistor R2. The ability togenerate and adjust and appropriate timing circuit is known to one ofordinary skill in the art.

In one embodiment of the pulse forming network 300 of FIG. 3, thedischarge timing of the last capacitor units of the discharge sequenceis varied in order to further increase the shut off time. By way ofexample, a pulse forming network having 4 inductors (i.e., 4 modules) isdescribed. In this example, the components of FIG. 3 will be referred towith the addition of a fourth module (having a fourth inductor)identical to one of the other modules 302, 304, 306. The fourth moduleis referred to as M4 including an inductor L4, four capacitor units C1,C2, C3, C4 and four switches S1, S2, S3, S4. Accordingly, the lastcapacitor unit of each module (i.e., the last capacitor units in thedischarge sequence, in this case, capacitor units 311, 321, 331 and C4)is discharged such that each successive capacitor pulse resonates at ahigher frequency odd harmonic (which also has a lower amplitude) thanthe preceding discharge pulse in the sequence. This can be done in anattempt to emulate the back end of a square wave which can be expressedas the sum of an infinite number of odd harmonics each at (1/n)*sin(nα),where n is an odd integer (i.e., n=1, 3, 5, 7 . . . ). Thus, each higherfrequency odd harmonic has a frequency that is n times the fundamentalfrequency and (1/n) times the amplitude of the fundamental frequency.

For example, the discharge pulse from capacitor unit 321 resonates atthe third harmonic of the discharge pulse from capacitor unit 311 (whichis at the fundamental frequency). Likewise, the discharge pulse fromcapacitor unit 331 resonates at the fifth harmonic of the dischargepulse from capacitor unit 311. And, the discharge pulse from capacitorunit C4 resonates at the seventh harmonic of the discharge pulse fromcapacitor unit 311. This is due to the well known fact that a squarewaveform is the sum of the odd harmonics. Accordingly, the final 4pulses in the pulse sequence from the discharge capacitor units will addtogether to form a square waveform at the end of the output pulsewaveform. Advantageously, this drastically reduces wasted energy at theend of the output waveform. For example, in some embodiments, the wastedenergy may be reduced by as much as 70% or more.

In order that the discharge pulse from each of these last capacitorunits in the pulse sequence resonates as described above, in oneembodiment, the timing between subsequent pulses when discharging theselast capacitor units of the sequence is successively shortened. Forexample, capacitor unit 321 is discharged in about half of the typicalswitching period. Thus, the product of the capacitance of the capacitorunit 321 and the circuit inductance 326 is reduced to 1/9 of the valuefor 311, 316, plus the load 104 (the capacitance inductance product) toachieve resonance at the third harmonic using the relationship$\frac{1}{\sqrt{LC}}.$Likewise, the switching period between capacitor units 331 and 321 isfurther decreased such that the capacitor unit 331 has effectively 1/25of its capacitance inductance product for the fifth harmonic. And theswitching period between capacitor units C4 and 331 is even furtherdecreased such that the capacitor unit C4 has effectively 1/49 of itscapacitance inductance product for the seventh harmonic. In addition,especially with the final capacitor unit C4 in the switching sequence,the inductor value may be varied since it may be difficult to adjust thecapacitance of C4 to 1/49 of its value simply by decreasing the timing.For example, a portion of the inductor L4 could be shorted out (orbypassed) while decreasing the timing such that the output pulse is atthe desired odd harmonic, which is easily understood to one of ordinaryskill in the art.

It is understood that the exact timing provided to achieve the desiredresult that the last multiple pulses in the pulse sequence are oddharmonics that add to form a square wave may need to be slightly variedfor a specific application to achieve the proper shut off time.Advantageously, by further decreasing the shut off time, very littleenergy is wasted at the end of the output pulse waveform. Thus, theenergy storage requirements of the pulse forming network may be designedto more closely match that the pulse requirements of the load. That is,the pulse forming network does not have to be oversized to account forwasted energy.

Referring next to FIG. 7, a flowchart is shown illustrating the stepsperformed in accordance with one embodiment of the invention. Thismethod may be performed, for example, by any of the pulse formingnetworks described herein.

Initially, a pulse forming network is provided having a plurality ofcapacitor units, wherein multiple capacitor units are coupled to each ofa plurality of inductors, each inductor coupled to a load (Step 702).For example, the networks of FIGS. 3, 8 and 10-11 may be provided;however, it is understood that other pulse forming networks than thosespecifically described herein may be used. Next, each of the capacitorunits is charged to an appropriate voltage level (Step 704). Such may beaccomplished by coupling the capacitor units to an appropriate chargingpower supply.

Next the pulse forming network is ready to be discharged to form theoutput pulse waveform to a load. First, timing control signals aregenerated to control the sequential discharging of the capacitor unitsin the desired sequence at the proper timing (Step 706). In oneembodiment, a timing controller is used to generate such timing controlsignals and output them to the respective switches, which when closed,will discharge a particular capacitor unit. For example, a timingcircuit such as described in FIG. 6 may be used.

As a result of the timing control signals, the multiple capacitor unitscoupled to each inductor are non-simultaneously discharged to providemultiple non-simultaneous pulses through each inductor to the load andnot through other inductors coupled to the load (Step 708). As describedabove, this is understood to mean that the discharge current from agiven capacitor unit discharged to form a given pulse flows through itsgiven inductor to the load and not through other inductors on its pathto the load (not including stray currents induced in each of the otherinductors when discharging the given capacitor unit). Accordingly, eachof the inductors is coupled to the load such that the current flowingtherethrough does not pass through the other inductors on its path tothe load. For example, in preferred embodiments, multiple inductors arenot coupled in series to the load. Furthermore, the impedance of theload is very small relative to the impedance of the other inductors suchthat the discharge current from a given capacitor unit naturally flowsthrough a given inductor directly to the load, and not through the otherinductors. It is further noted that the load includes an inductance;however, this load inductance is distinct from the discharge inductorsthat are each coupled to the load.

For example, in FIG. 3, capacitor units 308, 309, 310 and 311 aredischarged at different times. In preferred embodiments, the pulsesthrough a given inductor do not overlap in time. For example, in oneembodiment of FIG. 4, the pulses 403, 406, 409 and 412 do not overlap intime. In other embodiments, at least a portion of one or more of thepulses through a given inductor overlap in time, e.g., pulses 403 and406 may overlap in time. In one embodiment, the multiple capacitor unitsare each discharged by the non-simultaneous closing of respectiveswitches coupled to the multiple capacitor units.

It is noted that in some embodiments, as a result of the timing controlsignals, at least two of the multiple capacitor units are simultaneouslydischarged to provide at least two simultaneously discharged pulsesthrough each inductor to the load and not through other inductorscoupled to the load. Thus, in a broad sense, Step 708 provides that atleast some (and in some embodiments, all) of the multiple capacitorunits coupled to each inductor are non-simultaneously discharged toprovide multiple non-simultaneous pulses through each inductor to theload and not through other inductors coupled to the load.

Furthermore, in some embodiments, capacitor units coupled to differentinductors are discharged at substantially the same time. That is, somecapacitor units coupled to different inductors may be discharged at ornear the same time. For example, during the first pulses of thesequence, the first two capacitor units of the sequence (each coupled todifferent inductors) are discharged at or near the same time in order todecrease the rise time of the pulse in order to better emulate a flattop pulse waveform.

Furthermore, in preferred embodiments, groups of the multiple capacitorunits coupled to a respective inductor each comprise one of a pluralityof energy storage modules. According to one example, a dischargesequence is provided where given capacitor unit of each energy storagemodule is sequentially discharged over time to provide a given pulsethrough each inductor. Then, after beginning the discharging of thegiven capacitor unit of the last sequential module, a subsequentcapacitor unit of each energy storage module is sequentially dischargedover time to provide a subsequent pulse through each inductor to theload. For example, in one embodiment of FIG. 3, capacitor units 308, 318and 328 are sequentially discharged. Then, after beginning to dischargecapacitor unit 328, capacitor units 309, 319 and 329 are sequentiallydischarged. Then, after beginning to discharge capacitor unit 329,capacitor units 310, 320 and 330 are sequentially discharged.

Furthermore, in some embodiments, the discharge timing is such that thelast capacitor units in the discharging sequence are discharged at asuccessively higher frequency to produce the last pulses of a pulsesequence, such that each of the last pulses resonates at a higherfrequency odd harmonic relative to a preceding pulse. Accordingly, thesum of the last pulses in the sequence substantially form a squarewaveform. This results in a faster shut off time for the output pulsewaveform. For example, in one embodiment of FIG. 3, capacitor unit 321is discharged through inductor 326 sooner such that the resulting pulseresonates at a third odd harmonic of the pulse from capacitor unit 311,while capacitor unit 331 is discharged through inductor 336 successivelysooner such that the resulting pulse resonates at a fifth odd harmonicof the pulse from capacitor unit 311. This may be affected by changingthe timing of the appropriate signals that cause the last multiplecapacitor units to discharge.

In additional embodiments, the timing of the discharging of thecapacitor units in the sequence of discharging is controlled in order toprovide the proper pulse waveform. This timing can be made to vary or beadjusted over the course of the pulse depending on the shape of thepulse waveform or the impedance of the load. For example, if thewaveform is a triangular waveform, the time interval between thedischarging of successive capacitor units may decrease until the midwaypoint, then begin to increase as the pulse waveform ramps down.Furthermore, in applications in which the load is a variable impedanceload, such as in a rail gun application, the timing may be adjusted toaccount for the variable impedance of the load. In one example, in arail gun application, the time interval between the discharging ofsuccessive capacitor units is increased or decreased as the impedance ofthe load changes in order to keep a constant acceleration of theprojectile. In one embodiment, as the impedance increases, the timeinterval between the discharging of successive capacitor units isdecreased.

Referring next to FIG. 8, a diagram of a pulse forming network 800according to another embodiment. The embodiment of FIG. 8 is similar tothat of FIG. 3, but with the addition of diodes in series with theswitches of each capacitor unit. That is, a diode 802 is located in aseries connection between each switch (e.g., switch 312) and arespective inductor (e.g., inductor 316). These blocking diodes 802function to prevent the switches from going through a voltage reversaland conducting in the opposite direction should they fail to commutate,which will cause some switches to burn up and fail. This feature isparticularly useful when a given switch coupling a capacitor to oneinductor is intentionally closed before a previous capacitor unitcoupled to that inductor is not fully discharged. For example, asdescribed above, switch 312 closes to discharge capacitor unit 308through the inductor 316 to the load 104. The cycle continues asdescribed above, i.e., switches 322 and 332 are closed, and then switch313 is closed. In some instances, it may be desirable to close switch313 before capacitor unit 308 is fully discharged such that switch 312has not opened back up yet. In this case, if switch 313 is closed, thediode 802 will prevent the switch from going through a voltage reversaland thus, block current from flowing back into capacitor unit 308. Thus,according to several embodiments, a given switch coupling a givencapacitor unit to a given inductor may be closed prior to the fulldischarge of a capacitor unit associated with a previously closed switchto the same inductor. It is also noted that such diodes 802 provide thesame benefit when two or more switches coupling capacitor units to agiven inductor are closed at the same time (substantiallysimultaneously).

It is noted that these diodes 802 are optional. Many types of switchesare able to handle voltage reversal and thus, do not need diodes 802 toblock current flow. For example, SCRs or spark gaps do not need diodes802. Additionally, at low voltage, most switches will not need diodes802. In other words, the diodes 802 are optional depending on thecapabilities of the switch and/or the operation of the network.

FIG. 9 is a schematic diagram of a rail gun application using a pulseforming network to provide energy to launch a projectile in accordancewith several embodiments. A pulse forming network 900, which can be anyof the networks described herein, provides pulsed energy to the rail gunapparatus 902. A rail gun is a launching device that moves an armature904 or projectile along two rails of a launch barrel and projects thearmature at high speed out of the barrel. The current pulses from thenetwork 900 are coupled to the rails of the rail gun at the breach end.Each rail has a variable impedance, which is illustrated as a series ofresistances and inductances. Accordingly, the rail gun is a variableimpedance load. 902A illustrates the armature at the breach end. Whenenergy is applied to the rails, the armature is accelerated through thebarrel and projected out of the barrel. 902B illustrates the armature atthe muzzle end of the barrel as it is leaving the barrel. In thisapplication, it is desirable that the network 900 produce relativelysquare pulse waveform with as little residual energy left at the end ofthe pulse, which is timed to occur as the armature reaches the muzzleend of the rail gun. Excess energy in the rails at the muzzle endresults in muzzle flash, which requires the use of muzzle suppressors.As described above, according to many embodiments, the pulse formingnetworks described herein produce considerably less wasted energy (e.g.,see wasted energy 212 of the conventional pulse forming network of FIG.2). In many embodiments, there is a 50% or more reduction in wastedenergy, which in this application, wasted energy at the muzzle mayresult in muzzle flash. The following description provides additionalways to further reduce or eliminate muzzle flash without using flashsuppressors through the use of an active muzzle shunt circuit accordingto several embodiments.

Referring next to FIG. 10, a diagram is shown of a pulse forming networkaccording to a further embodiment for use in an application in whichexcess energy at the end of the pulse waveform is to be removed. In thisembodiment, the pulse forming network 800 is as illustrated in FIG. 8with the optional diodes 802 in series with each switch. The rail gun isschematically illustrated as rail gun 1002 comprising a variableimpedance load 1004. Although the pulse forming network 800 is coupledto the rail gun at the breach end, it is schematically shown as beingvariably connected from the breach end to the muzzle end. This isbecause the impedance of the rail gun changes from the perspective ofthe pulse forming network 800 as the projectile or armature moves alongthe rails. A muzzle shunt capacitor unit 1006 (generically referred toas a shunt capacitor unit) is provided and is coupled to the muzzle endof the rail gun via a shunt switch 1008. It is noted that the shuntcapacitor unit can be one or more different capacitors. In order toeliminate any residual energy that might contribute to muzzle flash, theshunt capacitor unit 1006 is coupled to the charging circuit 502 (notshown in FIG. 10) and charged to a voltage of a polarity opposite thatof the energy storage capacitor units of the pulse forming network. Asthe armature 904 nears or reaches the muzzle end, the shunt switch 1008closes and shunt current flows away from the muzzle into the shuntcapacitor unit 1006. In other words, the shunt capacitor unit isswitched to absorb the excess energy in the variable impedance load fromthe discharging of the plurality of capacitor units. Advantageously,through the proper voltage level of the shunt capacitor 1006, there isno excess energy left to product a muzzle flash. Ideally, there will bezero current on the muzzle end as the armature 904 passes through themuzzle end.

Referring next to FIG. 11, a diagram is shown of a pulse forming networkaccording to another further embodiment for use in an application inwhich excess energy at the end of the pulse waveform is to be removedwith an active shunt circuit. In this embodiment, rather than using aseparate shunt capacitor unit, one or more of the energy storagecapacitor units also function as shunt capacitors. As illustrated, eachof the capacitor units 328, 329, 330 and 331 is also coupled to themuzzle end of the variable impedance load (e.g., rail gun 1002) by ashunt switch (e.g., shunt switches 1102, 1104, 1106 and 1108). In thisembodiment, the capacitor units of the module 306 have two functions.They function as energy storage capacitors and they also function toshunt the muzzle current. The modules 302 and 304 operate as describedabove. However, module 306 does not include an anti-reversing diode orfree-wheeling diode (i.e., diode 344 is not included). Thus, when thecapacitor units of the module 306 are discharged, they go through avoltage reversal and become charged to an opposite polarity as the othercapacitor units. As the armature nears the muzzle end, the shuntswitches are closed to start the flow of muzzle shunt current into thecapacitor units of the module 306. Thus, in a broad sense, a shuntcapacitor (e.g., capacitor units 328, 329, 330 and 331) is charged to anopposite polarity and a shunt switch switches the shunt capacitor to thevariable impedance load to absorb excess energy in the load from thedischarging of the capacitor units. In this case, the shunt capacitorunit/s are also some of the energy storage capacitor units, whereas inthe embodiment of FIG. 10, the shunt capacitor unit is a separatecapacitor unit (not one of the energy storage capacitor units). In theembodiment of FIG. 11, the capacitor units of module 306 are allowed togo through a voltage reversal in order to charge them to an oppositepolarity (e.g., since there is no anti-reversing diode in this module).Additionally, a diode 1110 is coupled between the muzzle end and theshunt switches in order to keep the charge on the shunt capacitor units.It is noted that although it is not shown, a similar diode may becoupled between the switch 1008 and the muzzle end in FIG. 10.

In some variations, the switches 1102, 1104, 1106 and 1106 may beswitched at the same or different times. Additionally, less than all ofthe capacitor units of module 306 may be coupled to the muzzle of therail gun. Furthermore, the capacitor units of any of the modules 302,304 and 306 may be used for the shunt capacitor units, i.e., it does nothave to be the last module. Depending on the energy at the muzzle, theshunt capacitor units may include capacitor units from multiple modules.It has been found that in some applications, about 30% of the energybank of capacitor units is needed to shunt the excess energy. In suchcases, about 30% of the capacitor units will be allowed to go through avoltage reversal to function as shunt capacitors. In the embodiments ofboth FIGS. 10 and 11, if the muzzle shunt capacitor unit/s store aboutthe same energy as that stored inductively in the rail gun, the inductorcurrent and the capacitor voltage will both reach zero at approximatelythe same time causing all electrical activity in the circuit to stop.

Referring next to FIG. 12, a diagram is shown of a pulse forming network1200 in accordance with several embodiments in which one or more stagesof the network resembles a traditional pulse forming network stage. Itis noted that not all components are labeled since they are similar tothose described above. In this embodiment, one or more stages or modulesof the pulse forming network 1200 resemble traditional pulse formingnetwork stages or modules. For example, as illustrated the pulse formingnetwork includes three traditional energy storage modules 102 ₁, 102 ₂and 102 ₃ together with three stages or modules of the pulse formingnetworks as described above (e.g., modules 302, 304 and 306 asillustrated). In this embodiment, the capacitor units of each module ofpulse forming networks 100 and 800 discharge through their respectiveinductors 110 _(n), 316, 326 and 336 to the load 104. In one embodiment,the discharging sequence is as follows: bank of capacitors 106 ₁ isdischarged, then bank of capacitors 106 ₂, then bank of capacitors 106₃, then the capacitor units of modules 302, 304 and 306 in a variety ofsequences such as described above. This embodiment may be useful forapplications such as for driving a rail gun in which a fast rise time inthe pulse waveform is needed, but a faster shut off time is desired. Thetraditional pulse forming network stages or modules 112 _(n) provide theenergy at the beginning of the pulse waveform and the modules 302, 304and 306 provide the energy to the load at the end of the pulse waveform.Advantageously, as described above, the modules 302, 304 and 306 aredischarged as variously described above and result in a faster shut offtime with less residual energy than the conventional pulse formingnetwork modules.

It is noted that although three conventional modules 102 _(n) areillustrated, it is understood that there may be any number of suchmodules, e.g., at least one conventional stage through which multiplecapacitors are discharged simultaneously through a single inductor.Furthermore, although three modules 302, 304 and 306 as described hereinare illustrated, it is understood that there may be any number of suchmodules, e.g., at least two modules (at least two inductors) throughwhich at least some of multiple capacitors coupled to the load through asingle inductor are non-simultaneously discharged through the singleinductor. Similar to that described above, a charging circuit (notshown) is coupled to all capacitors in the network to charge them to theappropriate voltage. Additionally, as timing control circuit (not shown)is included to control the discharging of the respective capacitorunits. In other words, the timing control circuit causes the propertiming of the closing of the appropriate switches to discharge theappropriate capacitor units.

It is noted that in some embodiments, the location of the traditionalpulse forming network module/s may be varied within the pulse formingnetwork 1200. For example, if a very fast rise time is needed and aslower shut off time is needed in the pulse waveform produced by thenetwork 1200, the modules 302, 304 and 306 could be positioned todischarge before the conventional modules 102 _(n), i.e., the pulseforming network 800 would occur before the pulse forming network 100.

It is noted that in this embodiment, the inductors 110 _(n) of themodules 102 _(n) are larger than the inductors of modules 302, 304 and306 since there is a larger capacitance being switched therethrough at agiven time. In some embodiments, due to the length of the connectionfrom the modules 302, 304 and 306 to the load 104 (which in someapplications may be tens of feet) one or more of the inductors 316, 326and 336 may not be required to be discrete inductors. That is, thenatural inductance present in the connection from the modules 302, 304and 306 to the load provides an inductance. Due to the presence of thelarger inductors in the network 100, less inductance is required innetwork 800.

Furthermore, as described above, the voltage level of one or more of thecapacitor units of the network 1200 may be charged to different levels.For example, in one embodiment, the voltage level of capacitor unitsdischarging early in the sequence are charged to a lower voltage levelthat those capacitor units discharging later in the pulse waveform. Inembodiments using semiconductor stacks to function as the switches, thisallows for fewer switching devices (e.g., thyristors) to be needed foreach module 102 _(n) of the network 100, since the hold-off voltage isminimized. Additionally, typically, the first stage or module of thenetwork has the most demanding switch requirements. Thus, by having thecapacitor unit/s of the first few modules charged to a lower voltagethan subsequent modules, the requirements of the switching devices areeased, e.g., less expensive switching devices can be used. In oneembodiment, at least about 30-40% fewer thyristors are needed bycharging the capacitors of the network 100 to a lower voltage. In a railgun application, this advantageously allows for lower voltages to beused in the first stages and higher voltages to be used in the laterstages. It is noted that any of the various networks described hereinmay be operated such that one or more of the capacitor units of thepulse forming network are intentionally charged at different voltagelevels.

Referring next to FIG. 13, a diagram is shown of one embodiment of thepulse forming network of FIG. 12 for use in a rail gun application. Thenetwork 1300 of FIG. 13 represents one example of the network of FIG. 12in a rail gun application. Pulse forming network 1302 is a conventionalpulse forming network 100 having three stages or modules 102 ₁, 102 ₂and 102 ₃ including capacitor banks C1, C2 and C3. It is understood thateach of C1-C3 are multiple capacitors. Pulse forming network 1304 is anetwork similar to those described herein in which at least some of thecapacitor units coupled to a given inductor are non-simultaneouslydischarged by the switches. It is noted that not all components of thenetwork 1300 are labeled since they are the same as those describedabove. The first three modules of the network 1300 are conventionalpulse forming stages and the last two modules of the network 1300 are inaccordance with several embodiments described herein. The inductors L1,L2, L3, L4 and L5 are each coupled to the breach end of the rail gun1002. In this example, C1 has a value of 0.9 Farads (F), C2 has a valueof 0.1 F, C3 has a value of 0.1 F, C4 has a value of 0.05 F, C5 has avalue of 0.12 F, C6 has a value of 0.15 F, C7 has a value of 0.25 F andC8 has a value of 0.35 F. Furthermore, L1 has an inductance of 900nanoHenries (nH), L2 has an inductance of 1 microH, L3 has an inductanceof 250 nH, L4 has an inductance of 250 nH and L5 has an inductance of250 nH.

As illustrated in FIG. 14, the capacitor units of the network 1302 arecharged to a different (i.e., lower) voltage than the capacitor units ofthe network 1304. That is, C1-C3 are charged to about 5.8 kilovoltswhile C4-C8 are charged to about 11.1 kilovolts. Thus, this embodimentillustrates charging the first stages of the network 1300 to a lowervoltage than the final stages of the network, which provides a fast shutoff time for the rail gun application. FIG. 14 illustrates the timing ofthe discharging of the capacitor units of the network 1300. That is, thecapacitor units are discharged (by the closing of the appropriate switchcontrolled by a timing circuit) in the following order: C1, C2, C3, C4,C5, C6, C7 and then C8. Additionally, the timing between the dischargingof successive capacitor units is varied in some cases, for example, thetime between C1 and C2 is different than the time between C2 and C3.Likewise, the time between C4 and C5 is different than the time betweenC7 and C8. It is noted that the load of the rail gun is a variableimpedance load as described above.

FIG. 15 illustrates the current pulses provided by the pulse formingnetwork of FIG. 13 including the output pulse waveform 1500 inaccordance with one embodiment. Each pulse is labeled with the inductorthan provides the pulse. As can be seen, L1 provides the first pulse,then L2, then L3, then L4, then L5, then L4 (it is pulsed again bydischarging the second capacitor unit in the module 302), then L5 (it ispulsed again by discharging the second capacitor unit of the module304), and finally, L4 (which is pulsed again by discharging the thirdcapacitor unit of the module 304). The sum of these current pulses isrepresented by the output pulse waveform 1500, which represents thecurrent flowing in the load (i.e., in the rails of the rail gun). As canbe seen, the output pulse waveform provides a substantially squarewaveform. It is noted that the slope of the end of the pulse waveform(at shut off) shown at 1502 is considerably steeper than would beprovided by a conventional pulse forming network (i.e., the currentdecreases faster than would a traditional pulse forming network). Thisprovides for significantly less residual energy at the muzzle end of therail gun. It is noted that the current pulse from C1 through L1 islarger than the pulses from C2 and C3 since C1 has a higher capacitancethan C2 or C3. In view of the description herein, it is appreciated thatone could vary the timing of the discharging of capacitor units(overlapping or not, simultaneous discharge or not, etc.) and/or thecharge voltages of one or more of the capacitor units to produce adesired output pulse waveform. In other embodiments, the network 1304could be switched prior to the network 1302. It is also noted that thenumber of modules of both networks 1302 and 1304 can be varied accordingto the implementation. Furthermore, other techniques may be applied inaddition to this circuit to limit or removed excess energy at the muzzleend that could cause muzzle flash. For example, the muzzle end could beshorted, the timing of the last pulses may be such that little residualenergy remains or active shunt circuits as described herein can be addedto absorb any excess energy at the muzzle end.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. A capacitor based pulse forming network comprising: a plurality ofinductors adapted to be coupled to a load; a plurality of capacitorunits; a plurality of switches, each switch coupling a respectivecapacitor unit to a respective inductor, wherein multiple capacitorunits are coupled to each inductor by separate switches; and theplurality of switches are adapted to non-simultaneously discharge atleast some of the multiple capacitor units to provide non-simultaneouspulses through a given inductor to the load and not through otherinductors; wherein the non-simultaneous pulses form at least a portionof an output pulse waveform to the load.
 2. The network of claim 1wherein the plurality of switches are adapted to simultaneouslydischarge others of the multiple capacitor units to provide simultaneouspulses through the given inductor to the load and not through the otherinductors.
 3. The network of claim 1 wherein a first switch is adaptedto discharge one of the multiple capacitor units coupled to one inductorat substantially the same time as a second switch is adapted todischarge one of the multiple capacitor units coupled to anotherinductor.
 4. The network of claim 1 further comprising: a chargingcircuit coupled to each capacitor unit.
 5. The network of claim 1further comprising: a timing controller coupled to each switch, thetiming controller adapted to output a signal at an appropriate time tocause each switch to discharge a respective capacitor unit.
 6. Thenetwork of claim 1 further comprising: an anti-reversing diode coupledto each inductor, the anti-reversing diode coupled to a given inductorfor limiting voltage reversal across discharged capacitor units.
 7. Thenetwork of claim 1 wherein the non-simultaneous pulses through the giveninductor do not overlap in time with each other.
 8. The network of claim1 wherein a portion of at least two of the non-simultaneous pulsesthrough the given inductor overlap in time with each other.
 9. Thenetwork of claim 1 wherein the non-simultaneous pulses through the giveninductor are non-simultaneous with pulses through the other inductors.10. The network of claim 1 wherein plurality of switches are adapted tosequentially discharge the plurality of capacitor units.
 11. The networkof claim 1 wherein the plurality of switches are adapted to dischargethe last capacitor units in a discharging sequence at a successivelyhigher frequency to produce the last pulses of a pulse sequence, suchthat each of the last pulses resonates at a higher frequency oddharmonic relative to a preceding pulse, such that sum of the last pulsessubstantially comprises a square waveform, wherein resulting a fastershut off time for the output pulse waveform.
 12. The network of claim 1further comprising an anti-reversing diode coupled between each switchand its respective capacitor.
 13. The network of claim 1 wherein groupsof the multiple capacitor units coupled by a respective switch to arespective inductor each comprise one of a plurality of energy storagemodules.
 14. The network of claim 13 wherein the plurality of switchesare adapted to: sequentially discharge a first capacitor unit of eachenergy storage module over time to provide a first pulse through eachinductor to the load and not through inductors of other energy storagemodules; and sequentially discharge, after beginning the sequentialdischarge of the first capacitor unit of each energy storage module, asecond capacitor unit of each energy storage module over time to providea second pulse through each inductor to the load and not through theinductors of the other energy storage modules.
 15. The network of claim13 wherein the plurality of switches are adapted to: sequentiallydischarge a first capacitor unit of each energy storage module over timeto provide a first pulse through each inductor to the load and notthrough inductors of other energy storage modules; and sequentiallydischarge, after beginning the discharge of the first capacitor unit ofthe last sequential energy storage module, a subsequent capacitor unitof each energy storage module over time to provide a subsequent pulsethrough each inductor to the load and not through the inductors of theother energy storage modules, wherein the subsequent pulse does notoverlap in time with the first pulse of each energy storage module. 16.The network of claim 15 wherein the plurality of switches are adaptedto: repeat the sequential discharge of additional subsequent capacitorunits to provide additional subsequent pulses through each inductor tothe load until all of the plurality of capacitor units have beendischarged.
 17. The network of claim 15 wherein the plurality ofswitches are further adapted to: sequentially discharge a last capacitorunit of a given energy storage module at a higher frequency such that alast pulse of the last capacitor unit resonates at a higher frequencyodd harmonic relative to a last pulse of a sequentially preceding lastcapacitor unit of a sequentially preceding energy storage module,wherein causing a faster shut off time for the output pulse waveform.18. The network of claim 13 wherein the plurality of switches areadapted to: discharge one of the multiple capacitor units coupled to agiven inductor; and discharge another one of the multiple capacitorunits coupled to the given inductor after a start of the discharging ofthe one of the multiple capacitor units and before a voltage of the oneof the multiple capacitor units reaches zero.
 19. The network of claim13 wherein the plurality of switches are adapted to: discharge one ofthe multiple capacitor units coupled to a given inductor; and dischargeanother one of the multiple capacitor units coupled to the giveninductor after a voltage of the one of the multiple capacitor unitsreaches zero.
 20. The network of claim 13 wherein the load is a variableimpedance load and the plurality of capacitor units are adapted to becharged to a voltage at a polarity, the network further comprising: ashunt capacitor unit adapted to be charged to a voltage at an oppositepolarity of the plurality of capacitor units; and a shunt switch adaptedto couple the shunt capacitor unit to the variable impedance load,wherein the shunt switch is adapted to switch the shunt capacitor unitto the variable impedance load to absorb excess energy in the variableimpedance load from the discharging of the plurality of capacitor units.21. The network of claim 20 wherein the shunt capacitor unit comprisesone of the plurality of capacitor units.
 22. The network of claim 20wherein the shunt capacitor is not one of the plurality of capacitorunits.
 23. The network of claim 13 wherein the load is a variableimpedance load, the network further comprising: at least one shuntswitch adapted to couple at least one capacitor unit of at least one ofthe plurality of energy storage modules to the variable impedance load,wherein the at least one capacitor unit is allowed to go through avoltage reversal after discharging through its respective inductor andbe charged to an opposite polarity, wherein the at least one shuntswitch is adapted to switch the at least one capacitor unit to thevariable impedance load to absorb excess energy in the variableimpedance load from the discharging of the plurality of capacitor units.24. The network of claim 1 wherein at least some of the plurality ofcapacitor units are charged to different voltage levels.
 25. The networkof claim 1 wherein at least one of the plurality of capacitor unitsadapted to be discharged in time near an end of the output pulsewaveform are charged to a higher voltage level than ones of theplurality of capacitor units adapted to be discharged prior in time. 26.The network of claim 13 further comprising at least one additionalenergy storage module comprising, the additional energy storage modulecomprising: at least one additional inductor adapted to be coupled tothe load; a plurality of additional capacitor units coupled to each ofthe at least one additional inductor; a switch coupling the plurality ofadditional capacitor units to a respective additional inductor, eachswitch adapted to simultaneously discharge the plurality of additionalcapacitor units to provide an additional pulse through the respectiveadditional inductor to the load; wherein the additional pulse forms atleast a portion of the output pulse waveform to the load.
 27. Thenetwork of claim 26 wherein the at least one additional energy storagemodule is adapted to be discharged prior to discharging of the pluralityof capacitor units.
 28. A method for providing a pulse waveform to aload comprising: charging a plurality of capacitor units, whereinmultiple capacitor units are coupled to each of a plurality ofinductors, each inductor coupled to the load; and non-simultaneouslydischarging at least some of the multiple capacitor units to providenon-simultaneous pulses through a given inductor to the load and notthrough other inductors; wherein the non-simultaneous pulses form atleast a portion of the pulse waveform.
 29. The method of claim 28further comprising: simultaneously discharging others of the multiplecapacitor units to provide simultaneous pulses through the giveninductor to the load and not through the other inductors.
 30. The methodof claim 28 further comprising: discharging one of the multiplecapacitor units coupled to one inductor at substantially the same timeas discharging one of the multiple capacitor units coupled to anotherinductor.
 31. The method of claim 28 further comprising: receivingtiming signals at appropriate times to trigger the non-simultaneousdischarging.
 32. The method of claim 28 further comprising: limitingvoltage reversal across discharged capacitor units.
 33. The method ofclaim 28 wherein the non-simultaneous pulses through the given inductordo not overlap in time with each other.
 34. The method of claim 28wherein a portion of at least two of the non-simultaneous pulses throughthe given inductor overlap in time with each other.
 35. The method ofclaim 28 wherein the non-simultaneous pulses through the given inductorare non-simultaneous with pulses through the other inductors.
 36. Themethod of claim 28 further comprising: sequentially discharging theplurality of capacitor units.
 37. The method of claim 28 wherein thenon-simultaneous discharging step comprises: sequentially dischargingthe multiple capacitor units to provide sequential pulses through thegiven inductor to the load and not through other inductors.
 38. Themethod of claim 28 further comprising: discharging the last capacitorunits in a discharging sequence at a successively higher frequency toproduce the last pulses of a pulse sequence, such that each of the lastpulses resonates at a higher frequency odd harmonic relative to apreceding pulse, such that sum of the last pulses substantiallycomprises a square waveform, wherein resulting a faster shut off timefor the output pulse waveform.
 39. The method of claim 28 wherein thenon-simultaneously discharging step comprises: non-simultaneouslyclosing respective switches, each switch coupling each of the multiplecapacitor units to the given inductor.
 40. The method of claim 28further comprising: limiting voltage reversal across the respectiveswitches.
 41. The method of claim 28 wherein groups of the multiplecapacitor units coupled to a respective inductor each comprise one of aplurality of energy storage modules.
 42. The method of claim 41 furthercomprising: sequentially discharging a first capacitor unit of eachenergy storage module over time to provide a first pulse through eachinductor to the load and not through inductors of other energy storagemodules; and sequentially discharging, after beginning the sequentialdischarging of the first capacitor unit of each energy storage module, asecond capacitor unit of each energy storage module over time to providea second pulse through each inductor to the load and not through theinductors of the other energy storage modules.
 43. The method of claim41 further comprising: sequentially discharging a first capacitor unitof each energy storage module over time to provide a first pulse througheach inductor to the load and not through inductors of other energystorage modules; and sequentially discharging, after beginning thedischarging of the first capacitor unit of the last sequential energystorage module, a subsequent capacitor unit of each energy storagemodule over time to provide a subsequent pulse through each inductor tothe load and not through the inductors of the other energy storagemodules, wherein the subsequent pulse does not overlap in time with thefirst pulse of each energy storage module.
 44. The method of claim 43further comprising: repeating the sequentially discharging thesubsequent capacitor units for additional subsequent capacitor units toprovide additional subsequent pulses through each inductor to the loaduntil all of the plurality of capacitor units have been discharged. 45.The method of claim 43 further comprising: sequentially discharging alast capacitor unit of a given energy storage module at a higherfrequency such that a last pulse of the last capacitor unit resonates ata higher frequency odd harmonic relative to a last pulse of asequentially preceding last capacitor unit of a sequentially precedingenergy storage module, wherein causing a faster shut off time for theoutput pulse waveform.
 46. The method of claim 41 further comprising:discharging one of the multiple capacitor units coupled to a giveninductor; and discharging another one of the multiple capacitor unitscoupled to the given inductor after a start of the discharging of theone of the multiple capacitor units and before a voltage of the one ofthe multiple capacitor units reaches zero.
 47. The method of claim 41further comprising: discharging one of the multiple capacitor unitscoupled to a given inductor; and discharging another one of the multiplecapacitor units coupled to the given inductor after a voltage of the oneof the multiple capacitor units reaches zero.
 48. The method of claim 41wherein the load is a variable impedance load and the plurality ofcapacitor units are adapted to be charged to a voltage at a polarity,the method further comprising: charging a shunt capacitor unit to avoltage at an opposite polarity of the plurality of capacitor units; andcoupling the shunt capacitor unit to the variable impedance load toabsorb excess energy in the variable impedance load from the dischargingof the plurality of capacitor units.
 49. The method of claim 48 whereinthe shunt capacitor unit comprises one of the plurality of capacitorunits.
 50. The network of claim 48 wherein the shunt capacitor is notone of the plurality of capacitor units.
 51. The method of claim 41wherein the load is a variable impedance load, the method furthercomprising: allowing at least one capacitor unit of at least one of theplurality of energy storage modules to go through a voltage reversalafter discharging through its respective inductor and to be charged toan opposite polarity, coupling the at least one capacitor unit to thevariable impedance load to absorb excess energy in the variableimpedance load from the discharging of the plurality of capacitor units.52. The method of claim 28 wherein the charging step comprises chargingat least some of the plurality of capacitor units to different voltagelevels.
 53. The method of claim 28 wherein the charging step comprisescharging at least one of the plurality of capacitor units adapted to bedischarged in time near an end of the output pulse waveform to a highervoltage level than ones of the plurality of capacitor units adapted tobe discharged prior in time.
 54. The method of claim 41 furthercomprising: providing at least one additional energy storage modulecomprising at least one additional inductor coupled to the load and aplurality of additional capacitor units coupled to each of the at leastone additional inductor, wherein multiple capacitor units are coupled toeach of a plurality of inductors; charging the plurality of additionalcapacitor units; simultaneously discharging the plurality of additionalcapacitor units coupled to a respective additional inductor to providean additional pulse through the respective additional inductor to theload; wherein the additional pulse form at least a portion of the outputpulse waveform.
 55. The method of claim 54 wherein the simultaneouslydischarging step occurs prior to the non-simultaneously dischargingstep.
 56. The method of claim 28 further comprising: discharging theplurality of capacitor units, the discharging step including thenon-simultaneous discharging step; and controlling a timing of thedischarging of the capacitor units in order that the pulse waveform havea predetermined shape.
 57. The method of claim 28 wherein thecontrolling the timing step further comprising: adjusting the timing ofthe discharging while discharging in response a variable impedance ofthe load.
 58. A capacitor based pulse forming network comprising: meansfor charging a plurality of capacitor units, wherein multiple capacitorunits are coupled to each of a plurality of inductors, each inductorcoupled to the load; and means for non-simultaneously discharging atleast some of the multiple capacitor units to provide non-simultaneouspulses through a given inductor to the load and not through otherinductors; wherein the non-simultaneous pulses form at least a portionof the pulse waveform.